We have made those flights with time to spare: make sure you have the earliest luggage tags for disembarkation. There will be three for 7 a.m. and if you don't get one of those go to the pursers desk, or the cabin steward seems to have extras (on RCCL). We used cabs. Absolutately not problem getting one, no traffic to speak off. It didn't take much more than 20-25 minutes once we were in the cab. Customs and luggage claim seemed faster that early as well, no back log yet!